Contamination of potable water and inadequate access to purified potable water fit for human consumption is an alarming issue across the world. Contamination of potable water with inorganic ions and heavy metals, such as arsenic contamination and fluoride contamination, is especially harmful. Arsenic and fluoride contaminations, which are usually of geological origins, are mainly prevalent with ground water. Arsenic contamination through drinking water may cause cancer of skin, lungs, urinary bladder, and kidney, as well as other skin diseases. The current applicable regulations of the U.S. Environmental Protection Agency set the maximum limits of arsenic at 10 parts per billion (ppb) in drinking water, although compared to the rest of the United States, western states have more systems with arsenic levels greater than this standard. High fluoride concentration in ground water beyond the permissible limit of 1.5 parts per million (ppm) is an acute toxicological problem. Prolonged ingestion of high quantities of fluoride can lead to dental or skeletal fluorosis.
Some purification means must be employed to remove arsenic and control the level of fluoride in drinking water prior to consumption. The problem is compounded by the presence of minerals, including carbonates, which interfere with many purification schemes and systems. Particularly with water obtained from areas with geologic evidence of volcanic activity, both high arsenic levels and high mineral content, including carbonates, are typical.
There have been a number of systems used to remove arsenic and other heavy metals from water, including primarily reverse osmosis, column purification, and hydroxide precipitation. Many of these processes provide acceptable results only within narrow and restrictive parameters. In addition, many if not most of these processes are costly and comparatively inefficient.
Conventionally, Magnesium Oxide (MgO) is used for water purification as MgO is proven to be very effective in adsorbing arsenic and fluoride ions when these ions come in contact with the surface of MgO. Further, MgO is also abundant in nature, thereby making it easily available at affordable prices. While MgO is effective for arsenic and fluoride removal from water, its tendency to form paste or slurry, due to formation of magnesium hydroxide when contacted with water, is one of the main drawbacks in water purification applications. Hence when MgO is used for purifying water in a purifying system or a medium, the flow rate of the purified water decreases slowly and stops eventually requiring that the MgO be removed from the system.
Therefore, there is a need to develop a technology for water purification that provides effective removal of arsenic and fluoride from water, while avoiding one or more of the above-referenced drawbacks.